@article{altaqui_schrickx_gyurek_sen_escuti_brendan t. o'connor_kudenov_2022, title={Cephalopod-inspired snapshot multispectral sensor based on geometric phase lens and stacked organic photodetectors}, volume={61}, ISSN={["1560-2303"]}, DOI={10.1117/1.OE.61.7.077104}, abstractNote={Abstract. Multispectral imaging (MSI) is a valuable sensing modality for applications that require detecting a scene’s chemical characteristics. Existing MSI techniques utilize a filter wheel or color filter arrays, which are subject to reduced temporal or spatial resolution. In this work, we present a cephalopod-inspired multispectral organic sensor (CiMOS) based on geometric phase lenses (GPLs) and organic photovoltaics (OPVs) to enable aberration-based color sensing. We mimic the approach by which animals with single-type photoreceptors perceive colors via chromatic aberration. The intrinsic chromatic aberration of GPLs allows for multispectral sensing by stacking precisely patterned OPVs within specific spectrally dependent focal lengths. We provide simulations and a proof of concept of the CiMOS and highlight its advantages, including its simple design and snapshot multi-color detection using only a single axial position. Experimental results demonstrate the sensor’s ability to detect four colors with full width at half maximum spectral resolution as low as 35 nm.}, number={7}, journal={OPTICAL ENGINEERING}, author={Altaqui, Ali and Schrickx, Harry and Gyurek, Sydney and Sen, Pratik and Escuti, Michael and Brendan T. O'Connor and Kudenov, Michael}, year={2022}, month={Jul} }
 @article{altaqui_schrickx_sen_li_rech_lee_balar_you_kim_escuti_et al._2021, title={Bio-inspired spectropolarimetric sensor based on tandem organic photodetectors and multi-twist liquid crystals}, volume={29}, ISSN={["1094-4087"]}, url={https://doi.org/10.1364/OE.431858}, DOI={10.1364/OE.431858}, abstractNote={Simultaneous spectral and polarimetric imaging enables versatile detection and multimodal characterization of targets of interest. Current architectures incorporate a 2×2 pixel arrangement to acquire the full linear polarimetric information causing spatial sampling artifacts. Additionally, they suffer from limited spectral selectivity and high color crosstalk. Here, we demonstrate a bio-inspired spectral and polarization sensor structure based on integrating semitransparent polarization-sensitive organic photovoltaics (P-OPVs) and liquid crystal polymer (LCP) retarders in a tandem configuration. Color tuning is realized by leveraging the dynamic chromatic retardation control of LCP films, while polarization sensitivity is realized by exploiting the flexible anisotropic properties of P-OPVs. The structure is marked by its ultra-thin design and its ability to detect spectral and polarimetric contents along the same optical axis, thereby overcoming the inherent limitations associated with conventional division-of-focal plane sensors.}, number={26}, journal={OPTICS EXPRESS}, publisher={The Optical Society}, author={Altaqui, Ali and Schrickx, Harry and Sen, Pratik and Li, Lingshan and Rech, Jeromy and Lee, Jin-Woo and Balar, Nrup and You, Wei and Kim, Bumjoon J. and Escuti, Michael and et al.}, year={2021}, month={Dec}, pages={43953–43969} }
 @article{altaqui_sen_schrickx_rech_lee_escuti_you_kim_kolbas_brendan t. o'connor_et al._2021, title={Mantis shrimp-inspired organic photodetector for simultaneous hyperspectral and polarimetric imaging}, volume={7}, ISSN={["2375-2548"]}, url={https://doi.org/10.1126/sciadv.abe3196}, DOI={10.1126/sciadv.abe3196}, abstractNote={Semitransparent polarization-sensitive organic detectors reveal unprecedented degrees of freedom for multidimensional imaging. Combining hyperspectral and polarimetric imaging provides a powerful sensing modality with broad applications from astronomy to biology. Existing methods rely on temporal data acquisition or snapshot imaging of spatially separated detectors. These approaches incur fundamental artifacts that degrade imaging performance. To overcome these limitations, we present a stomatopod-inspired sensor capable of snapshot hyperspectral and polarization sensing in a single pixel. The design consists of stacking polarization-sensitive organic photovoltaics (P-OPVs) and polymer retarders. Multiple spectral and polarization channels are obtained by exploiting the P-OPVs’ anisotropic response and the retarders’ dispersion. We show that the design can sense 15 spectral channels over a 350-nanometer bandwidth. A detector is also experimentally demonstrated, which simultaneously registers four spectral channels and three polarization channels. The sensor showcases the myriad degrees of freedom offered by organic semiconductors that are not available in inorganics and heralds a fundamentally unexplored route for simultaneous spectral and polarimetric imaging.}, number={10}, journal={SCIENCE ADVANCES}, publisher={American Association for the Advancement of Science (AAAS)}, author={Altaqui, Ali and Sen, Pratik and Schrickx, Harry and Rech, Jeromy and Lee, Jin-Woo and Escuti, Michael and You, Wei and Kim, Bumjoon J. and Kolbas, Robert and Brendan T. O'Connor and et al.}, year={2021}, month={Mar} }
 @article{schrickx_sen_booth_altaqui_burleson_rech_lee_biliroglu_gundogdu_kim_et al._2021, title={Ultra-High Alignment of Polymer Semiconductor Blends Enabling Photodetectors with Exceptional Polarization Sensitivity}, volume={10}, ISSN={["1616-3028"]}, DOI={10.1002/adfm.202105820}, abstractNote={Photodetectors that can sense not only light intensity but also light's polarization state add valuable information that is beneficial in a wide array of applications. Polymer semiconductors are an attractive material system to achieve intrinsic polarization sensitivity due to their anisotropic optoelectronic properties. In this report, the thermomechanical properties of the polymer semiconductors PBnDT‐FTAZ and P(NDI2OD‐T2) are leveraged to realize bulk heterojunction (BHJ) films with record in‐plane alignment. Two polymer blends with distinct weight average molar masses (Mw) are considered and either a strain‐ or rub‐alignment process is applied to align the polymer blend films. Optimized processing yields films with dichroic ratios (DR) of over 11 for the high Mw system and nearly 17 for the low Mw system. Incorporating the aligned films into photodetectors results in a polarized photocurrent ratio of 15.25 with corresponding anisotropy ratio of 0.88 at a wavelength of 530 nm, representing the highest reported photocurrent ratio for photodiodes that can operate in a self‐powered regime. The demonstrated performance showcases the ability of polymer semiconductors to achieve BHJ films with exceptional in‐plane polymer alignment, enabling high performance polarization sensitive photodetectors for incorporation into novel device architectures.}, journal={ADVANCED FUNCTIONAL MATERIALS}, author={Schrickx, Harry M. and Sen, Pratik and Booth, Ronald E. and Altaqui, Ali and Burleson, Jacob and Rech, Jeromy J. and Lee, Jin-Woo and Biliroglu, Melike and Gundogdu, Kenan and Kim, Bumjoon J. and et al.}, year={2021}, month={Oct} }
 @article{yang_sen_brendan t. o'connor_kudenov_2020, title={Optical crosstalk and off-axis modeling of an intrinsic coincident polarimeter}, volume={59}, ISSN={["2155-3165"]}, DOI={10.1364/AO.59.000156}, abstractNote={Polarimeters have broad applications in remote sensing, astronomy, and biomedical imaging to measure the emitted, reflected, or transmitted state of polarization. An intrinsic coincident (IC) full-Stokes polarimeter was previously demonstrated by our group, in a free space configuration, by using stain-aligned polymer-based organic photovoltaics. To minimize the model's complexity, these were tilted to avoid crosstalk from back-reflections. We present a theoretical model of a monolithic IC polarimeter that considers the back-reflection's influence for on-axis light. The model was validated using a monolithic four-detector polarimeter, which achieved an error of less than 3%. Additionally, an off-axis model was produced and validated for a simpler two detector polarimeter, demonstrating an error between the TM and TE polarized components of less than 3% for angles spanning an 18° incidence cone.}, number={1}, journal={APPLIED OPTICS}, author={Yang, Ruonan and Sen, Pratik and Brendan T. O'Connor and Kudenov, Michael W.}, year={2020}, month={Jan}, pages={156–164} }
 @article{yang_sen_o'connor_kudenov_2020, title={Optimization of an intrinsic coincident polarimeter and quantitative architectural comparison of different polarimeter techniques}, volume={59}, ISSN={["1560-2303"]}, DOI={10.1117/1.OE.59.2.024111}, abstractNote={Abstract. Polarimeters have broad applications in remote sensing, astronomy, and biomedical imaging to measure a scene’s polarization state. An intrinsic coincident (IC) full-Stokes polarimeter was previously demonstrated and optimized to achieve high temporal and spatial resolution. We optimized the IC polarimeter by introducing additional waveplates or measurement channels and compared it with existing polarimeter architectures under signal-independent Gaussian noise and signal-dependent Poisson noise. The quantitative comparison of noise variances showed that the IC and division-of-amplitude polarimeters have the lowest noise variances due to their higher signal collection ability. Both polarimeters have a factor of 2 and 2 improved signal-to-noise ratio, in the S0 component, for Gaussian and Poisson noises, respectively, as compared to division of time, division of focal plane, and division of aperture polarimeters. While the division of amplitude and IC polarimeters outperforms other approaches, the IC polarimeter has a significantly simpler design, potentially allowing for cost-effective, high-performance polarimetric imaging.}, number={2}, journal={OPTICAL ENGINEERING}, author={Yang, Ruonan and Sen, Pratik and O'Connor, Brendan and Kudenov, Michael}, year={2020}, month={Feb} }
 @article{sun_song_balar_sen_kline_brendan t. o'connor_2019, title={Impact of Substrate Characteristics on Stretchable Polymer Semiconductor Behavior}, volume={11}, ISSN={["1944-8252"]}, DOI={10.1021/acsami.8b16457}, abstractNote={Stretchable conductive polymer films are required to survive not only large tensile strain but also stay functional after the reduction in applied strain. In the deformation process, the elastomer substrate that is typically employed plays a critical role in response to the polymer film. In this study, we examine the role of a polydimethylsiloxane (PDMS) elastomer substrate on the ability to achieve stretchable PDPP-4T films. In particular, we consider the adhesion and near-surface modulus of the PDMS tuned through UV/ozone (UVO) treatment on the competition between film wrinkling and plastic deformation. We also consider the role of PDMS tension on the stability of films under cyclic strain. We find that increasing the near-surface modulus of the PDMS and maintaining the PDMS in tension throughout the cyclic strain process promote plastic deformation over film wrinkling. In addition, the UVO treatment increases film adhesion to the PDMS resulting in a significantly reduced film folding and delamination. For a 20 min UVO-treated PDMS, we show that a PDPP-4T film root-mean-square roughness is consistently below 3 nm for up to 100 strain cycles with a strain range of 40%. In addition, although the film is plastically deforming, the microstructural order is largely stable as probed by grazing incidence X-ray scattering and UV-visible spectroscopy. These results highlight the importance of neighboring elastomer characteristics on the ability to achieve stretchable polymer semiconductors.}, number={3}, journal={ACS APPLIED MATERIALS & INTERFACES}, author={Sun, Tianlei and Song, Runqiao and Balar, Nrup and Sen, Pratik and Kline, R. Joseph and Brendan T. O'Connor}, year={2019}, month={Jan}, pages={3280–3289} }
 @article{sen_yang_rech_feng_ho_huang_so_kline_you_kudenov_et al._2019, title={Panchromatic All-Polymer Photodetector with Tunable Polarization Sensitivity}, volume={7}, ISSN={["2195-1071"]}, DOI={10.1002/adom.201801346}, abstractNote={In this report, a high‐performance all‐polymer organic photodetector that is sensitive to linearly polarized light throughout the visible spectrum is demonstrated. The active layer is a bulk heterojunction composed of an electron donor polymer PBnDT‐FTAZ and acceptor polymer P(NDI2OD‐T2) that have complementary spectral absorption resulting in efficient detection from 350 to 800 nm. The blend film exhibits good ductility with the ability to accommodate large strains of over 60% without fracture. This allows the film to undergo large uniaxial strain resulting in in‐plane alignment of both polymers making the film optically anisotropic and intrinsically polarization sensitive. The films are characterized by UV–vis spectroscopy and grazing incidence wide‐angle X‐ray scattering showing that both polymers have similar in‐plane backbone alignment and maintain packing order after being strained. The films are integrated into devices and characterized under linear polarized light. The strain‐oriented detectors have maximum photocurrent anisotropies of 1.4 under transverse polarized light while maintaining peak responsivities of 0.21 A W−1 and a 3 dB cutoff frequency of ≈1 kHz. The demonstrated performance is comparable to the current state of the art all‐polymer photodetectors with the added capability of polarization sensitivity enabling new application opportunities.}, number={4}, journal={ADVANCED OPTICAL MATERIALS}, author={Sen, Pratik and Yang, Ruonan and Rech, Jeromy J. and Feng, Yuanxiang and Ho, Carr Hoi Yi and Huang, Jinsong and So, Franky and Kline, R. Joseph and You, Wei and Kudenov, Michael W. and et al.}, year={2019}, month={Feb} }
 @article{park_nallainathan_mondal_sen_dickey_2018, title={Light-Induced Buckles Localized by Polymeric Inks Printed on Bilayer Films}, volume={14}, ISSN={["1613-6829"]}, url={https://doi.org/10.1002/smll.201704460}, DOI={10.1002/smll.201704460}, abstractNote={Buckling instabilities generate microscale features in thin films in a facile manner. Buckles can form, for example, by heating a metal/polymer film stack on a rigid substrate. Thermal expansion differences of the individual layers generate compressive stress that causes the metal to buckle over the entire surface. The ability to dictate and confine the location of buckle formation can enable patterns with more than one length scale, including hierarchical patterns. Here, sacrificial "ink" patterned on top of the film stack localizes the buckles via two mechanisms. First, stiff inks suppress buckles such that only the non-inked regions buckle in response to infrared light. The metal in the non-inked regions absorbs the infrared light and thus gets sufficiently hot to induce buckles. Second, soft inks that absorb light get hot faster than the non-inked regions and promote buckling when exposed to visible light. The exposed metal in the non-inked regions reflects the light and thus never get sufficiently hot to induce buckles. This second method works on glass substrates, but not silicon substrates, due to the superior thermal insulation of glass. The patterned ink can be removed, leaving behind hierarchical patterns consisting of regions of buckles among non-buckled regions.}, number={20}, journal={SMALL}, publisher={Wiley}, author={Park, Sungjune and Nallainathan, Umaash and Mondal, Kunal and Sen, Pratik and Dickey, Michael D.}, year={2018}, month={May} }
 @article{sen_xiong_zhang_park_you_ade_kudenov_brendan t. o'connor_2018, title={Shear-Enhanced Transfer Printing of Conducting Polymer Thin Films}, volume={10}, ISSN={["1944-8244"]}, DOI={10.1021/acsami.8b09968}, abstractNote={Polymer conductors that are solution-processable provide an opportunity to realize low-cost organic electronics. However, coating sequential layers can be hindered by poor surface wetting or dissolution of underlying layers. This has led to the use of transfer printing where solid film inks are transferred from a donor substrate to partially fabricated devices using a stamp. This approach typically requires favorable adhesion differences between the stamp, ink, and receiving substrate. Here, we present a shear-assisted organic printing (SHARP) technique that employs a shear load on a post-less polydimethylsiloxane (PDMS) elastomer stamp to print large-area polymer films that can overcome large unfavorable adhesion differences between the stamp and receiving substrate. We explore the limits of this process by transfer printing poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) films with varied formulation that tune the adhesive fracture energy. Using this platform, we show that the SHARP process is able to overcome a 10-fold unfavorable adhesion differential without the use of a patterned PDMS stamp, enabling large-area printing. The SHARP approach is then used to print PEDOT:PSS films in the fabrication of high-performance semitransparent organic solar cells.}, number={37}, journal={ACS APPLIED MATERIALS & INTERFACES}, author={Sen, Pratik and Xiong, Yuan and Zhang, Qanqian and Park, Sungjune and You, Wei and Ade, Harald and Kudenov, Michael W. and Brendan T. O'Connor}, year={2018}, month={Sep}, pages={31560–31567} }
 @article{yang_sen_o'connor_kudenov_2017, title={Intrinsic coincident full-Stokes polarimeter using stacked organic photovoltaics}, volume={56}, ISSN={["2155-3165"]}, DOI={10.1364/ao.56.001768}, abstractNote={An intrinsic coincident full-Stokes polarimeter is demonstrated by using strain-aligned polymer-based organic photovoltaics (OPVs) that can preferentially absorb certain polarized states of incident light. The photovoltaic-based polarimeter is capable of measuring four Stokes parameters by cascading four semitransparent OPVs in series along the same optical axis. This in-line polarimeter concept potentially ensures high temporal and spatial resolution with higher radiometric efficiency as compared to the existing polarimeter architecture. Two wave plates were incorporated into the system to modulate the S3 Stokes parameter so as to reduce the condition number of the measurement matrix and maximize the measured signal-to-noise ratio. Radiometric calibration was carried out to determine the measurement matrix. The polarimeter presented in this paper demonstrated an average RMS error of 0.84% for reconstructed Stokes vectors after normalized to S0. A theoretical analysis of the minimum condition number of the four-cell OPV design showed that for individually optimized OPV cells, a condition number of 2.4 is possible.}, number={6}, journal={APPLIED OPTICS}, author={Yang, Ruonan and Sen, Pratik and O'Connor, B. T. and Kudenov, M. W.}, year={2017}, month={Feb}, pages={1768–1774} }
 @article{yang_sen_o'connor_kudenov_2017, title={Intrinsic coincident full-Stokes polarimeter using stacked organic photovoltaics and architectural comparison of polarimeter techniques}, volume={10407}, ISBN={["978-1-5106-1271-6"]}, ISSN={["1996-756X"]}, DOI={10.1117/12.2273885}, abstractNote={An intrinsic coincident full-Stokes polarimeter is demonstrated by using stain-aligned polymer-based organic photovoltaics (OPVs) which can preferentially absorb certain polarized states of incident light. The photovoltaic-based polarimeter is capable of measuring four stokes parameters by cascading four semitransparent OPVs in series along the same optical axis. Two wave plates were incorporated into the system to modulate the S3 stokes parameter so as to reduce the condition number of the measurement matrix. The model for the full-Stokes polarimeter was established and validated, demonstrating an average RMS error of 0.84%. The optimization, based on minimizing the condition number of the 4-cell OPV design, showed that a condition number of 2.4 is possible. Performance of this in-line polarimeter concept was compared to other polarimeter architectures, including Division of Time (DoT), Division of Amplitude (DoAm), Division of Focal Plane (DoFP), and Division of Aperture (DoA) from signal-to-noise ratio (SNR) perspective. This in-line polarimeter concept has the potential to enable both high temporal (as compared with a DoT polarimeter) and high spatial resolution (as compared with DoFP and DoA polarimeters). We conclude that the intrinsic design has the same ~√2 SNR advantage as the DoAm polarimeter, but with greater compactness.}, journal={POLARIZATION SCIENCE AND REMOTE SENSING VIII}, author={Yang, Ruonan and Sen, Pratik and O'Connor, B. T. and Kudenov, M. W.}, year={2017} }
 @article{roy_awartani_sen_o'connor_kudenov_2016, title={Intrinsic coincident linear polarimetry using stacked organic photovoltaics}, volume={24}, ISSN={["1094-4087"]}, DOI={10.1364/oe.24.014737}, abstractNote={Polarimetry has widespread applications within atmospheric sensing, telecommunications, biomedical imaging, and target detection. Several existing methods of imaging polarimetry trade off the sensor's spatial resolution for polarimetric resolution, and often have some form of spatial registration error. To mitigate these issues, we have developed a system using oriented polymer-based organic photovoltaics (OPVs) that can preferentially absorb linearly polarized light. Additionally, the OPV cells can be made semitransparent, enabling multiple detectors to be cascaded along the same optical axis. Since each device performs a partial polarization measurement of the same incident beam, high temporal resolution is maintained with the potential for inherent spatial registration. In this paper, a Mueller matrix model of the stacked OPV design is provided. Based on this model, a calibration technique is developed and presented. This calibration technique and model are validated with experimental data, taken with a cascaded three cell OPV Stokes polarimeter, capable of measuring incident linear polarization states. Our results indicate polarization measurement error of 1.2% RMS and an average absolute radiometric accuracy of 2.2% for the demonstrated polarimeter.}, number={13}, journal={OPTICS EXPRESS}, author={Roy, S. Gupta and Awartani, O. M. and Sen, P. and O'Connor, B. T. and Kudenov, M. W.}, year={2016}, month={Jun}, pages={14737–14747} }